1. Field of the Invention
This invention relates to a mammography compression device, and more particularly to a compression paddle which provides a more uniform compression to a woman's breast while preventing too much compression at the chest wall and yet providing enough compression towards the nipple end of the breast.
2. Description of Related Art
Mammography systems utilize a compression paddle which is used to compress the breast of a patient intermediate a support plate and the compression paddle. Good compression of the breast is necessary for good quality mammographic images. Good compression spreads apart the breast structures which reduces superimposed structures and spreads apart the breast tissue permitting better visualization of abnormalities.
Good compression of the breast improves mammographic image quality in several ways. Breast thickness is decreased, reducing radiation exposure time. This can eliminate blurring of the image due to motion. Lower x-ray energy is required and this produces higher contrast images while limiting patient exposure to radiation.
In the most common prior art breast compression device, the compression paddle is rigidly fixed to a frame and positioned so as to have a single compression surface which parallels a breast support platform surface. These prior art compression devices used with conventional mammography systems produce non-uniform breast compression with the greatest compression closest to the chest wall and the least compression towards the nipple where the breast is not as thick. These compression paddles also unfortunately permit movement of the breast tissue in the mid breast and in the nipple end of the breast during imaging which causes blurring of the image, because of insufficient compression. Since exposure times are typically measured on the order of seconds, even though the patient may not move observably, small movement as well as the heart beating can blur images over time. Those images taken with longer exposure times, such as about two or more seconds, are particularly often adversely affected. Additionally, these prior art compression paddles can cause patient discomfort near the chest wall where the compression surface applies the greatest compression.
A number of other compression paddles have been developed in order to attempt to overcome some of the problems associated with the most common prior art design.
One prior art breast compression device has a single planar compression surface that is not used parallel to the an image detector. The apparatus comprises a compression paddle pivotally connected to a frame at a pivot point located between the chest wall end and the nipple end. The paddle may be positioned at one of a plurality of angles relative to the support surface. When the non-parallel planar surface is angled toward the nipple from the chest wall, the breast tissue can be squeezed or pushed out of the x-ray field back towards and effectively into the chest wall. The result is that tissue, which may contain a tumor is not imaged. Nevertheless, this design more effectively compresses the nipple end of the breast than the parallel planar surface. An example of this type may be seen in U.S. Pat. No. 5,706,327.
Another compression system is disclosed in U.S. Pat. No. 3,971,950 to Evans, Jul. 27, 1976. This patent discloses a mammographic compression and positioning device which is independent of the x-ray system. The compression surface of the paddle has a curved lower surface with both a concave and a convex surface. The position of the paddle is adjustable in a plurality of directions. These curves are not believed to optimally compress the breast as the nipple end of the breast is undercompressed due to the concave portion located above the nipple end. The chest wall end would also be undercompressed. An additional drawback would be the breast tissue at chest wall end would tend to be pushed back out of the field of view of the imager.
Another compression paddle system has a paddle which comes down at an angle. This was produced by Planmed of Helsinki, Finland. During the first phase of compression, the chest wall side of the upper paddle is angled toward the image detector at the start of compression. As the paddle descends and starts to compress the breast, the paddle begins to level out. At completion of the compression, the paddle is level or parallel to the image detector. Since the paddle is level at the end of the process, it is not believed to be optimally oriented to compress the breast.
Another known compression device for a mammography system is disclosed in U.S. Pat. No. 5,506,877. This patent discloses a compression paddle, which is pivotally connected within the support frame by a pivot connection. The pivot connection is located on a chest wall side of the support frame. The compression paddle is substantially horizontal to the detector and is rotatable around the pivot connection. During the initial compression the compression paddle begins substantially parallel to said detector. As force is applied the paddle angles toward the detector during final compression. The breast appears to dictate the angle of compression, not the radiologist in this design. Furthermore, due to the conical shape of the breast, during final compression the paddle will end up angled downwardly from the chest wall to the nipple thereby pushing the breast toward the chest wall, possibly pushing some of the breast out of an image.
Another known compression paddle system was produced by Trex Medical Corporation for Bennett Contour mammography systems (Trex Medical Corporation, Product Brochure, January 1997). This compression apparatus comprises a compression paddle pivotally connected to a frame at a pivot point located at the chest wall end. Rotation about the pivot point is allowed so that an operator may select the paddle angle. The paddle itself was comprised of two planar surfaces which meet at an angle of about nine degrees. The planar surface closest to the chest wall extends a length of about one inch away from the breast with the other planar surface extending from there past the nipple.
While the Bennett paddle achieves improved compression of the breast without significantly displacing any breast tissue backward out of the field of view at the chest wall end, this device still has a number of disadvantages. Specifically, the approximate 9° angle between the two planar surfaces is believed to be so great that it effectively forms a valley where the two angular surfaces meet. The breast located below this valley receives suboptimal compression in a zone where the largest percentage of cancers are detected. Almost one half of all breast cancers are located within the posterior one third of the breast which is where this “dead zone” occurs with the Bennett paddle. The breast is very thick in this area which in itself often makes good imaging difficult. If there is suboptimal compression here, small cancers might not be detected. A need therefore exists to optimally compress the breast within this zone to remove this potential “dead zone” from images taken.
Another known compression device for a mammography system is disclosed in U.S. Pat. No. 5,851,180 to Crosby et al., Dec. 22, 1998. This patent discloses an apparatus having first and second compression surfaces that experience a lateral translation as they move towards one another. In addition, the first and second compression surfaces may be tilted slightly relative to a plane orthogonal to the patient's chest wall to enhance the traction effect on the breast.
While significant strides have been made to provide a good compression system, a need still exists to provide an optimum paddle design. There are over twenty-five different types of breast cancer and many more abnormalities which could be confused as cancer. It only takes finding one additional cancer which would otherwise elude detection and go unnoticed to make a huge difference in the life of that one individual.